<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        div {
            border: 1px solid green;
        }
        .container { 
            width:100%; 
        }
        .wrapper {
            position:relative;
            padding-bottom: 56.25%;   // 16/9 = 0.5625;
            height:0;
            border: 1px solid red;
        }
        .content {
            position:absolute;
            top: 0;
            left: 0;
            width: 100%;
            height:100%;
            background:gray;
        }
    </style>
</head>
<body>

<div class="container">
    <div class="wrapper">
        <div class="content">content</div>
    </div>
</div>

    
</body>
</html>